Radiation detection system and method of analyzing an electrical pulse output by a radiation detector

ABSTRACT

A radiation detection system can include a photosensor to receive light from a scintillator via an input and to send an electrical pulse at an output in response to receiving the light. The radiation detection system can also include a pulse analyzer that can determine whether the electrical pulse corresponds to a neutron-induced pulse, based on a ratio of an integral of a particular portion of the electrical pulse to an integral of a combination of a decay portion and a rise portion of the electrical pulse. Each of the integrals can be integrated over time. In a particular embodiment, the pulse analyzer can be configured to compare the ratio with a predetermined value and to identify the electrical pulse as a neutron-induced pulse when the ratio is at least the predetermined value.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S. PatentApplication No. 61/286,512 entitled “Radiation Detection System andMethod of Analyzing an Electrical Pulse Output by a Radiation Detector,”by Menge et al., filed Dec. 15, 2009, which is assigned to the currentassignee hereof and incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure is directed to radiation detection systems andmethods of analyzing electrical pulses output by radiation detectors.

RELATED ART

Radiation detectors are used in a variety of industrial applications.For example, scintillators can be used for medical imaging and for welllogging in the oil and gas industry. Typically, scintillators havescintillator crystals made of an activated sodium iodide or othermaterial that is effective for detecting gamma rays or neutrons.Generally, the scintillator crystals are enclosed in casings or sleevesthat include a window to permit radiation-induced scintillation light topass out of the crystal package. The light passes to a light-sensingdevice, such as a photomultiplier tube. The photomultiplier tubeconverts the light photons emitted from the crystal into electricalpulses. The electrical pulses can be processed by associated electronicsand may be registered as counts that are transmitted to analyzingequipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes a block diagram illustrating a particular embodiment ofa radiation detection system.

FIG. 2 includes a block diagram illustrating an example embodiment ofthe pulse analyzer illustrated in FIG. 1.

FIG. 3 includes a plot illustrating a particular embodiment of a shapeof a gamma radiation-induced electrical pulse.

FIG. 4 includes a plot illustrating a particular embodiment of a shapeof a neutron-induced electrical pulse.

FIGS. 5 and 6 include plots illustrating another particular embodimentof a shape of a neutron-induced electrical pulse.

FIG. 7 includes a plot illustrating another particular embodiment of ashape of a neutron-induced electrical pulse.

FIG. 8 includes a flow diagram illustrating a particular embodiment of amethod of analyzing an electrical pulse output by a radiation detector.

FIG. 9 includes a flow diagram illustrating a particular embodiment of amethod of analyzing an electrical pulse output by a radiation detector.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive-or and not to an exclusive-or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Also, the use of “a” or “an” is employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one or at least one and the singular alsoincludes the plural, or vice versa, unless it is clear that it is meantotherwise. For example, when a single device is described herein, morethan one device may be used in place of a single device. Similarly,where more than one device is described herein, a single device may besubstituted for that one device.

FIG. 1 illustrates a particular embodiment of a radiation detectionsystem 100. The radiation detection system 100 can include ascintillator 101 coupled to a photosensor 105. In one embodiment, theradiation detection system 100 can include a light pipe 103. Though thescintillator 101, the light pipe 103, and the photosensor 105 areillustrated separate from each other, the scintillator 101 and thephotosensor 105 can be coupled to each other directly or via the lightpipe 103. In one embodiment, the scintillator 101 and the photosensor105 can be coupled to the light pipe 103 using an optical gel, bondingagent, fitted structural components, or any combination thereof.

The scintillator 101 can include a scintillating material 107 housedwithin a casing 113. The scintillating material 107 can include amaterial to detect neutrons, gamma radiation, other targeted radiation,or any combination thereof. For instance, the scintillating material 107can include a material suitable for use with a dual gamma/thermalneutron detector. In an embodiment, the scintillating material 107 caninclude an organic material, such as a scintillating substance within anorganic non-scintillating medium. For instance, the scintillatingmaterial can include ⁶Li, ¹⁰B, or ^(nat)Gd within an organic liquid,gel, or polymer. In another example, the scintillating material 107 caninclude a phosphor screen including ZnS, ⁶Li, a layer ofwavelength-shifting fiber, or any combination thereof. In anotherembodiment, the scintillating material 107 can include an inorganicmaterial, such as a Cs₂LiYCl₆, Cs₂LiYBr₆, Rb₂LiYCl₆, another Elpasolitecrystal, or another type of crystal.

In a particular embodiment, the scintillator 101 can include athermalyzer or neutron moderator to moderate fast neutrons into thermalneutrons for which ⁶Li or ¹⁰B have higher interaction cross sections.The neutron moderator can include, for example, polyethylene surroundingthe scintillator 101. In another embodiment, the ⁶Li or ¹⁰B can bedissolved in a hydrocarbon solvent that acts as a thermalyzer to slowfast neutrons to speeds compatible with scintillating materialsincluding ⁶Li or ¹⁰B.

The scintillator 101 can also include a reflector 109. In oneembodiment, the casing 113 can include a shock-absorbing member 111disposed between the casing 113 and the reflector 109. Further, thecasing 113 can include an output window 115 that is interfaced to an endof the scintillating material 107. The output window 115 can includeglass or another transparent or translucent material suitable to allowphotons emitted by the scintillator 101 to pass toward the photosensor105. In an illustrative embodiment, an optical interface, such as clearsilicone rubber, can be disposed between the scintillating material 107and the output window 115. The optical interface can be polarized toalign the reflective indices of the scintillating material 107 and theoutput window 115.

As illustrated, the light pipe 103 can be disposed between thephotosensor 105 and the scintillator 101 and can facilitate opticalcoupling between the photosensor 105 and the scintillator 101. In oneembodiment, the light pipe 103 can include a quartz light pipe, plasticlight pipe, or another light pipe. In another embodiment, the light pipe103 can comprise a silicone rubber interface that optically couples anoutput window 115 of the scintillator 101 with the input 108 of thephotosensor 105. In some embodiments, multiple light pipes can bedisposed between the photosensor 105 and the scintillator 101.

The photosensor 105 can comprise a photodiode, a photomultiplier tube(PMT), or a hybrid PMT that includes a photocathode and a semiconductorelectron sensor. The photosensor 105 can be housed within a tube orhousing made of a material capable of protecting electronics associatedwith the photosensor 105, such as a metal, metal alloy, other material,or any combination thereof.

The photosensor 105 can include an input 108 and an output 110, such asan interface to receive a coaxial cable or other article to transmitelectrical signals. The photosensor 105 can receive, via the input 108,light from the scintillator 101, other sources, or a combinationthereof. The photosensor 105 can be configured to send electrical pulsesfrom the output 110 to the pulse analyzer 120, in response to light thatthe photosensor 105 receives. The pulse analyzer 120 and its operationare described in further detail later in this specification. The pulseanalyzer 120 can be coupled to a pulse counter 130 that counts photonsreceived at the photosensor 105 based on electrical pulses output by thephotosensor 105 to the pulse analyzer 120. The pulse analyzer 120 mayalso be coupled to another pulse processing device 140. For example, thecounter 130 can comprise a neutron counter, and the pulse processingdevice 140 can comprise a gamma radiation counter.

In a particular, illustrative embodiment, the photosensor 105 can beconfigured to receive light from the scintillator 101 via the input 108.Photons included in the light can strike a photocathode 118 of thephotosensor 105 and transfer energy to electrons in a valence band ofthe photocathode 118. The electrons can become excited until they areemitted as electrons from a surface of the photocathode 118 that isopposite the input 108. In a particular embodiment, the surface of thephotocathode 118 can include a layer of electropositive material thatcan facilitate emission of the electrons from the surface of thephotocathode 118.

Electrons emitted by the photocathode 118 can be collected at an anodeof the photosensor 105, and an electrical pulse or signal can be sent tothe pulse analyzer 120 via the output 110. In an example, a firstvoltage 121, such as a supply voltage or other voltage, can be appliedto the photocathode 118. Electrons emitted from the surface of thephotocathode 118 can be accelerated, by the first voltage 121, to strikethe surface of an electron detector 119. In addition, a second voltage122, such as a reverse bias voltage or other voltage, can be applied tothe electron detector 119. Energy from electrons entering the electrondetector can produce carriers that are removed from the electrondetector 119 by the reverse bias voltage 122, creating an electricalpulse.

In a particular embodiment, the photosensor 105 can receive lightemitted by the scintillator 101 as a result of the scintillatingmaterial 107 receiving gamma radiation, neutrons, other targetedradiation, or any combination thereof. The photosensor 105 can send anelectrical pulse to the pulse analyzer 120 after receiving such light.The pulse analyzer 120 can be configured to analyze the electrical pulseand to determine whether the electrical pulse corresponds to a gammaradiation-induced electrical pulse or a neutron-induced electricalpulse.

In a particular embodiment, the pulse analyzer 120 can include a moduleor device, such as a field programmable gate array, another digitalcircuit, an analog circuit, or any combination thereof, to identify anelectrical pulse as corresponding to a neutron-induced electrical pulseor a gamma radiation-induced electrical pulse, based on a shape of theelectrical pulse. FIGS. 3 and 4 illustrate an example of differences inshape between a gamma radiation-induced electrical pulse and aneutron-induced electrical pulse. FIG. 3 illustrates a particularembodiment of a gamma radiation-induced electrical pulse 300. The pulse300 can have a relatively fast rise portion 304, which extends from athreshold 302 to a peak 305 of the electrical pulse 300. The pulse 300can have a relatively slow decay portion 306, which extends from thepeak 305 of the electrical pulse 300 down to the threshold 302.

FIG. 4, on the other hand, illustrates a particular embodiment of aneutron-induced electrical pulse 400. The pulse 400 can also have arelatively fast rise portion 404, which extends from a threshold 402 toa peak 405 of the electrical pulse 400. However, the pulse 400 can havea more gradual decay portion 406 than the decay portion 306 of the gammaradiation-induced electrical pulse 300.

In a particular embodiment, the pulse analyzer 120 can exploit thedifference in shape between electrical pulses and identify an electricalpulse as corresponding to a neutron-induced electrical pulse or a gammaradiation-induced electrical pulse, based on a ratio of an integral overtime of a particular portion of the electrical pulse, to an integralover time of a total pulse. The particular portion can include, forexample, a decay portion, a rise portion, another portion, or anycombination thereof that includes less than the total pulse. As usedherein, the phrase “total pulse” refers to a combination of the decayportion and a rise portion of the electrical pulse that are at or abovea threshold. The combination of the decay portion and the rise portioncan include a peak of the electrical pulse, an integration window arounda highest reading of the electrical pulse, or a combination thereof.

As an example of the calculated integrals, FIGS. 5 and 6 illustrateanother particular embodiment of a neutron-induced electrical pulse 500.In this example, the pulse analyzer 120 can calculate an integral of thedecay portion 508 over time, to determine an area 506, illustrated inFIG. 5, under the decay portion 508 and at or above the threshold 502.The integral can be calculated over a time that extends from a highestreading 504 down to the threshold 502, or from a pre-determined timeafter the highest reading 504 down to the threshold 502. Additionally,the pulse analyzer 120 can calculate an integral over time of the totalpulse at or above the threshold 502, to determine an area 510,illustrated in FIG. 6, under the shape of the electrical pulse and at orabove the threshold 502.

Though a peak 504 is illustrated in FIG. 5, the difficulty of findingwhere in time the peak 504 occurs may cause difficulties in determininga start of the decay portion 508 to be integrated (whether at the peak504 or subsequent to the peak 504) and in integrating the totalelectrical pulse at or above the threshold 502. As a result, varioustechniques to approximate the peak can be used for purposes ofintegrating the total pulse to find the area 510.

For example, as illustrated in FIG. 7, an electronic pulse has a peak704. Other than at the peak 704, the total area defined by theelectrical pulse between a starting time and an ending time can beapproximated by using the averages of each pair of two immediatelyadjacent readings and multiplying the averages times the correspondingtime differences between such pairs of readings. At the peak 704, suchan approximation may not be as accurate because no measurement may betaken at the peak 704 itself. Because the peak 704 may be higher thanthe highest reading obtained, using the average of two readings timesthe time difference would usually underestimate the area that includesthe peak 704.

To determine the area near the peak 704, the pulse analyzer 120 maydefine a peak integration window 706 that extends a certain amount oftime before, after, or a combination thereof, a highest reading, such asthe reading 720. The readings corresponding to the electrical pulse canbe analyzed to determine that reading 720 is the highest reading. Thepeak 704 may occur (1) at the highest known reading or (2) between thehighest measurement and either the measurement immediately before orimmediately after the highest known reading. Because the overall shapeof the electrical pulse is generally known (faster rise time compared toa slower decay time), the peak 704 may be determined to have occurredbetween the reading 720 (highest reading) and a reading 718 (readingimmediately before the highest reading), rather than between the reading720 and a reading 722 (reading immediately after the highest reading).Thus, the integration window 706 can be defined by the times at thereadings 718 and 720. In a particular embodiment, the integration window706 may be at most 2 ns wide. The pulse analyzer 120 or pulse processingdevice 140 may use the highest reading 720 by itself or even a highervalue when approximating the area within the integration window 706.Thus, the integration window 706 may more accurately estimate the totalarea, as compared to merely using averages of pairs of immediatelyadjacent readings (for example, the averages of the readings 718 and720) when determining the integral over time of the total pulse at orabove the threshold 702.

In another example, the peak can be approximated by calculating a slopeof the rise 712 from the threshold 702 to a highest known reading thatis continuous with the rise, and by calculating a slope of the decay 708from the threshold 702 to a highest known reading that is continuouswith the decay 708. The rise 712 and the decay 708 can each be extended,according to its slope, and the intersection of the two can beapproximated as the peak of the electrical pulse. Other techniques canbe used to account for the peak of the electrical pulse, such as asmoothing function that approximates a time at which the peak occurs.

After calculating the integrals, the pulse analyzer 120 can calculate aratio of the integral over time of the particular portion of theelectrical pulse to the integral over time of the total electrical pulseat or above the threshold. The pulse analyzer 120 can return the ratioas a variable and compare it to a predetermined value. If the ratio isat least the predetermined value, the electrical pulse can correspond toa neutron-induced electrical pulse. If the ratio is less than thepredetermined value, the electrical pulse can correspond to a gammaradiation-induced electrical pulse. Skilled artisans will recognize thatother positions of ratios relative to a threshold can indicate whetheran electrical pulse corresponds to a neutron-induced electrical pulse ora gamma radiation-induced electrical pulse.

The pulse analyzer 120 can be adapted to send an indicator to the pulsecounter 130 or the pulse processing device 140, which indicates that theelectrical pulse corresponds to a gamma radiation-induced electricalpulse or a neutron-induced electrical pulse. In an example, theindicator can be a one or a zero when the electrical pulse correspondsto a neutron-induced electrical pulse, and can be the other of one orzero when the electrical pulse corresponds to a gamma radiation-inducedelectrical pulse. The pulse analyzer 120 can send a one via an output132 and a zero via another output 134. In a non-limiting embodiment, thepulse counter 130 the pulse processing device 140, or another devicecommunicating with both, can generate separate neutron and gammaradiation spectra, based on indicators received from the pulse analyzer120.

In another embodiment, the indicator can be a replicate of theelectrical pulse. For instance, the pulse analyzer 120 can send ananalog output, such as an analog replicate of the electrical pulse oranother analog signal via an output 132, when the electrical pulsecorresponds to a neutron-induced electrical pulse. The pulse analyzer120 can send the replicate of the electrical pulse or another analogsignal via another output 134, when the electrical pulse corresponds toa gamma radiation-induced electrical pulse.

In a non-limiting embodiment, a threshold, a peak integration window, apredetermined value, another parameter, or any combination thereof canbe adjustable at the pulse analyzer 120. For instance, a parameter canbe adjusted based on a property of the scintillating material 107. In anexample, a threshold can be adjusted depending on a relative decay timefor a neutron-induced pulse compared to a relative decay time for agamma radiation-induced pulse, with respect to a particularscintillating material that is responsive to both neutrons and gammaradiation. If a threshold is set too low, pulse shape may be difficultto analyze for a scintillating material or application that has arelatively higher noise level. If the threshold is set too high,however, pulse shape may not be identifiable enough to distinguishneutron-induced pulses from gamma radiation-induced electrical pulsesfor a scintillating material characterized by a less intense electricalpulse. Thus, adjustment of the threshold can assist in pulseidentification by balancing reduction of noise with accuracy and speedof correctly identifying the pulse shape for different scintillatingmaterials.

In another example, the pulse analyzer 120 can include a fieldprogrammable gate array (FPGA)-based system that is adapted to calculateintegrals of the particular portion and the total pulse withinuser-definable windows. For instance, the FPGA-based system cancalculate the integral over time of the decay of the electrical pulsewithin a tail-window and calculate the integral over time of the totalelectrical pulse at or above the threshold within a total-window,respectively. The start and end of both the tail-window and thetotal-window can be variables whose values can be set by a user at runtime.

Many embodiments of pulse analyzers that output an electrical pulse,another analog signal or another indicator from a particular output of aplurality of outputs, based on a ratio of calculated integrals, arepossible. FIG. 2 illustrates an example embodiment of a pulse analyzer,such as the pulse analyzer 120 illustrated in FIG. 1. The pulse analyzer120 can include a signal splitter 204 that communicates with aphotosensor output 202. The splitter 204 is coupled to a pulse analysisdevice 206 and an analog delay circuit 208. In a particular embodiment,the pulse analysis device 206 can include an FPGA or another digitalcircuit, logic to perform functions associated with analyzing a shape orother characteristic of an electrical pulse, or any combination thereof.In an example, the pulse analysis device 206 can include an FPGA-baseddigital multichannel analyzer. The delay circuit 208 can include, forexample, a resistor delayed with a transistor or operational amplifier.Other delay circuits may be used. The pulse analysis device 206 and thedelay circuit 208 are coupled to an output control circuit 210, which iscoupled to an output 212 and another output 214. The pulse analysisdevice 206, the delay circuit 208, the output control circuit 210, theoutputs 212 and 214, or any combination thereof can be included within asingle housing.

In a particular embodiment, the splitter 204 can receive an electricalpulse from the photosensor output 202. The splitter 204 can send areplicate of the electrical pulse to the pulse analysis device 206, andthe splitter can send another replicate of the electrical pulse to theanalog delay circuit 208. The pulse shape analysis device 206 cancalculate an integral over time of a particular portion of theelectrical pulse and can calculate an integral over time of a totalpulse at or above a threshold. The pulse analysis device 206 cancalculate a ratio of the integral over time of the particular portion tothe integral over time of the total pulse and can compare the ratio to apredetermined value, in order to determine whether the electrical pulsecorresponds to a neutron-induced electrical pulse or a gammaradiation-induced electrical pulse. For instance, if the ratio is atleast the predetermined value, the electrical pulse can correspond tothe neutron-induced electrical pulse. Whereas, if the ratio is below thepredetermined value, the electrical pulse can correspond to the gammaradiation-induced electrical pulse.

In a particular embodiment, the pulse analysis device 206 can send alogic pulse to the output control circuit 210 when the electrical pulsecorresponds to a neutron-induced electrical pulse. In anotherembodiment, the pulse analysis device 206 can send a logic pulse to theoutput control circuit 210 when the electrical pulse corresponds to agamma radiation-induced electrical pulse. The output control circuit 210can receive the other replicate of the electrical pulse from the analogdelay circuit 208 after the pulse analysis device 206 has determinedwhether the electrical pulse corresponds to a neutron-induced electricalpulse or a gamma radiation-induced electrical pulse. The output controlcircuit 210 can determine whether to send the electrical pulse to theoutput 212 or the output 214 based on the logic pulse. For example, whenthe output control circuit 210 receives a logic pulse, it can send theother replicate of the electrical pulse to the output 212. When theoutput control circuit 210 does not receive a logic pulse, it can sendthe other replicate of the electrical pulse to the output 214. The pulseanalyzer 120 can thus output an analog replicate of the electrical pulsereceived from the photosensor output 202, via one of the outputs 212 and214, based on whether the electrical pulse corresponds to aneutron-induced electrical pulse or a gamma radiation-induced electricalpulse.

FIG. 8 illustrates a particular embodiment of a method of analyzing anelectrical pulse output by a radiation detector. At 800, a pulseanalyzer receives an electrical pulse from an output of a photosensor ata radiation detector. Moving to 802, the pulse analyzer replicates theelectrical pulse. Proceeding to 804, the pulse analyzer sends areplicate of the electrical pulse to a pulse analysis device and sendsanother replicate to an analog delay circuit. Continuing to 806, thepulse analysis circuit determines a ratio of an integral over time of aparticular portion of the electrical pulse, to an integral over time ofa combination of a total pulse at or above a threshold. Advancing to808, the pulse analysis circuit compares the ratio to a predeterminedvalue.

At 810, the pulse analysis device determines whether the electricalpulse corresponds to a neutron-induced pulse. If so, the method can moveto 812, and the pulse analysis device can send a logic pulse to anoutput control circuit. Proceeding to 814, the pulse analyzer can outputan analog replicate of the electrical pulse via an output. Returning to810, if the pulse analysis device determines that the electrical pulsedoes not correspond to a neutron-induced pulse, the method can move to816, and the pulse analysis device can send no logic pulse to the outputcontrol circuit. The method can proceed to 818, and the pulse analyzercan output an analog replicate of the electrical pulse via anotheroutput. The method can terminate at 820.

FIG. 9 illustrates another particular embodiment of a method ofanalyzing an electrical pulse output by a radiation detector, such as ananalysis performed by the pulse analysis device illustrated at 120 inFIG. 2 and referred to with respect to the electrical pulse asillustrated in FIG. 6. At 902, the pulse analysis device can receive areplicate of an electrical pulse. Moving to 904, the pulse analysisdevice can identify a total pulse at or above a threshold. For instance,the pulse analysis device can identify an earliest reading and a latestreading of the electrical pulse that are at or above the threshold. Thepulse analysis device can also determine an integration window relativeto a peak of the electrical pulse.

Proceeding to 906, the pulse analysis device can calculate an integralover a particular time period of a particular portion of the electricalpulse. The pulse analysis device can also calculate another integralover a larger time period to include most of the total pulse. For eachintegral, only those portions of the electrical pulse at or above thethreshold may be used. The other integral over the larger time periodmay include the peak integration window as previously described. In aparticular embodiment, background noise is subtracted from theelectrical pulse. Alternatively, a pulse offset can be set to zerobefore the integrals are calculated. Continuing to 908, the pulseanalysis device can determine a ratio of the integrals and compare theratio to a predetermined value. Advancing to 910, the pulse analysisdevice can determine whether the electrical pulse corresponds to aneutron-induced pulse. If so, the pulse analysis device can send a logicpulse to an output control circuit at 912. Otherwise, the pulse analysisdevice may not send a logic pulse to an output control circuit at 914.

At 916, in a non-limiting embodiment, the pulse analysis device candetermine whether it has received input to change a parameter of pulseanalysis. For instance, a threshold, a predetermined value, a peakintegration window, another parameter, or any combination thereof can beadjustable at the pulse analysis device. If the pulse analysis devicehas received input to change a parameter, the method can proceed to 918,and the pulse analysis can change the threshold, a predetermined value,the peak integration window, the other parameter, or any combinationthereof based on the input. The method terminates at 920.

In accordance with particular embodiments and structure disclosedherein, a radiation detection system is provided that can include apulse analyzer to identify an electrical pulse output by a photosensoras corresponding to a neutron-induced pulse or a gamma radiation-inducedpulse, by comparing a predetermined value to a ratio of an integral overtime of a particular portion of the electrical pulse, to an integralover time of a total pulse at or above a threshold over time(tail-to-total integral ratio). Neutron-induced pulses typically havelonger decay portions, for example, than gamma radiation-induced pulses,resulting in a larger ratio than the ratio for a gamma radiation-inducedpulse. Thus, if the ratio is at least the predetermined value, theelectrical pulse can correspond to the neutron-induced pulse, and if theratio is below the predetermined value, the electrical pulse cancorrespond to the gamma radiation-induced pulse.

Skilled artisans will recognize that a ratio of an integral over time ofthe total pulse at or above the threshold to an integral over time ofthe particular portion may be used. For example, a total-to-tailintegral ratio may be used, in which case a ratio that is at least apredetermined value can indicate that an electrical pulse corresponds toa gamma radiation-induced pulse.

In a particular embodiment, the pulse analyzer can output an analogreplicate of the electrical pulse via an output or another output, basedon whether the electrical pulse corresponds to a neutron-induced pulseor a gamma radiation-induced pulse.

In a particular embodiment, the pulse analyzer can be adjusted tocompliment virtually any organic or inorganic scintillator that issensitive to both neutrons and gamma radiation. For instance, aradiation detector using a CLYC (cerium-doped cesium lithium yttriumchloride elpasolite (Cs₂LiYCl₆(Ce))) scintillating material may emitelectrical pulses having a decay portion of approximately 1 μs for aneutron-induced pulse and a decay portion of approximately 100 ns for agamma radiation-induced electrical pulse. On the other hand, a radiationdetector using a phosphor screen based on ZnS(Ag) and ⁶Li as ascintillating material may emit electrical pulses having a decay portionof approximately 40 ns for a neutron-induced pulse and a decay portionof approximately 20 ns for a gamma radiation-induced electrical pulse.

In a particular embodiment, a user may adjust a start time, an end time,for a decay portion, a rise portion, a total pulse, or any combinationthereof, before determining integrals or ratios thereof. A predeterminedvalue can be adjusted to determine whether a ratio of integralsindicates that an electrical pulse corresponds to a neutron-inducedpulse or a gamma radiation-induced electrical pulse. In an example, auser utilizing CLYC as a scintillator may choose to calculate a tailintegral over a 300 ns portion of a decay, starting at or about a peakof an electrical pulse. A sample tail-to-total integral for a neutroninduced electrical pulse may be approximately 0.94 mV.ns/4.71 mV.ns, orapproximately 0.20. Whereas, a tail-to-total integral for a gammaradiation-induced electrical pulse may be 0.30 mV.ns/0.56 mV.ns, orapproximately 0.54. Thus, in this example, a user may choose to set thepredetermined value at 0.35, to determine whether a ratio of integralsindicates that an electrical pulse corresponds to a neutron-inducedpulse or a gamma radiation-induced electrical pulse.

In another example, a user utilizing ⁶Li and ZnS as a scintillatingmaterial may choose to calculate a tail integral over a 10 ns portion ofa decay, starting at or about a peak of an electrical pulse. A sampletail-to-total integral for a neutron induced electrical pulse may beapproximately 0.019 mV.ns/0.082 mV.ns, or approximately 0.236. Whereas,a tail-to-total integral for a gamma radiation-induced electrical pulsemay be 0.00163 mV.ns/0.00485 mV.ns, or approximately 0.3371. Thus, inthis example, a user may choose to set the predetermined value at 0.28,to determine whether a ratio of integrals indicates that an electricalpulse corresponds to a neutron-induced pulse or a gammaradiation-induced electrical pulse.

The example integration values and ratios described above are intendedonly to illustrate exemplary differences in ratios between electricalpulses induced by neutrons as opposed to gamma radiation and not tolimit the concepts described herein. Integral values and ratios may varysignificantly as a user changes scintillating materials and adjusts atime window over which a decay portion, rise portion, total pulse, orany combination thereof, is integrated. Hence, the ability of a user toadjust the predetermined value to evaluate a ratio provides the userwith the flexibility to account for scintillating material and for theuser's desire to include or exclude a variety of electrical pulseportions when determining whether an electrical pulse corresponds to aneutron-induced pulse, a gamma radiation-induced electrical pulse, anoise pulse or another pulse type.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described below. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Additionally, those skilled in the art willunderstand that some embodiments that include analog circuits can besimilarly implemented using digital circuits, and vice versa.

In a first aspect, a radiation detection system can include aphotosensor to receive light from a scintillator via an input and tosend an electrical pulse at an output in response to receiving thelight. The radiation detection system can also include a pulse analyzerthat can determine whether the electrical pulse corresponds to aneutron-induced pulse, based on a ratio of an integral of a particularportion of the electrical pulse to an integral of a combination of adecay portion and a rise portion of the electrical pulse. Each of theintegrals can be integrated over time. In an embodiment of the firstaspect, the particular portion can consist essentially of the decayportion. The pulse analyzer can be configured to compare the ratio witha predetermined value and to identify the electrical pulse as aneutron-induced pulse when the ratio is at least the predeterminedvalue.

In an embodiment of the first aspect, the particular portion consistsessentially of the decay portion. In another embodiment, the pulseanalyzer is configured to compare the ratio with a predetermined valueand to identify the electrical pulse as a neutron-induced pulse when theratio is at least the predetermined value. In a particular embodiment,the pulse analyzer is configured to compare the ratio with thepredetermined value, and identify the electrical pulse as a gammaradiation-induced pulse when the ratio is less than the predeterminedvalue. In another particular embodiment, the pulse analyzer isconfigured to return the ratio as a variable and to compare the variableto the predetermined value. In still another embodiment, the decayportion and the rise portion include portions of the electrical pulsethat are at or above a threshold. In a particular embodiment, thethreshold is adjustable at the pulse analyzer.

In a further embodiment of the first aspect, the combination of thedecay portion and the rise portion includes a peak of the electricalpulse. In still a further embodiment, the combination of the decayportion and the rise portion includes a peak integration window definedby a first time at that corresponds to a highest reading of theelectrical pulse and a second time that corresponds to a reading that isimmediately before or immediately after the highest reading. In aparticular embodiment, a peak integration window has a width that isadjustable at the pulse analyzer. In yet a further embodiment, the pulseanalyzer includes an FPGA. In a particular embodiment, the pulseanalyzer includes an FPGA-based multichannel analyzer.

In another embodiment of the first aspect, the pulse analyzer isconfigured to send an indicator to a pulse processing device, whereinthe indicator indicates whether the electrical pulse corresponds to theneutron-induced pulse or to the gamma radiation-induced pulse. In aparticular embodiment, the pulse analyzer is configured to send theindicator via a first output when the electrical pulse corresponds tothe neutron-induced pulse, and to send the indicator via a second outputwhen the electrical pulse corresponds to the gamma radiation-inducedpulse. In a more particular embodiment, the indicator is one or zerowhen the electrical pulse corresponds to the neutron-induced pulse, andwherein the indicator is the other of one or zero when the electricalpulse corresponds to the gamma radiation-induced pulse. In another moreparticular embodiment, the indicator includes a first replicate of theelectrical pulse. In an even more particular embodiment, the firstreplicate includes an analog replicate of the electrical pulse.

In another even more particular embodiment of the first aspect, thepulse analyzer includes a splitter to replicate the electrical pulse andto send the first replicate to a delay circuit and to send a secondreplicate to a pulse analysis device, and an output control circuit toreceive the first replicate from the delay circuit after the pulseanalysis device has calculated the integrals, wherein the output controlcircuit is configured to send the first replicate to the first outputafter receiving a logic pulse from the pulse analysis device and to sendthe first replicate to the second output when a logic pulse is notreceived from the pulse analysis device. In a still even more particularembodiment, the pulse analysis device is configured to send the logicpulse when the ratio is at least a predetermined value. In another stilleven more particular embodiment, the pulse analysis device and theoutput control circuit are within a single housing.

In a second aspect, a method can include receiving an electrical pulseat a pulse analyzer from a photosensor of a radiation detection device.The method can also include determining whether the electrical pulsecorresponds to a neutron-induced pulse or a gamma radiation-inducedpulse, based on a ratio of an integral of a particular portion of theelectrical pulse to an integral of a combination of a decay portion anda rise portion of the electrical pulse. Each of the integrals can beintegrated over time, and the decay portion and the rise portion can beabove a threshold. The method can also include sending an indicator to apulse processing device, the indicator identifying the electrical pulseas corresponding to a neutron-induced pulse or a gamma radiation-inducedpulse. In an embodiment of the second aspect, the particular portion canconsist essentially of the decay portion.

In an embodiment of the second aspect, the particular portion consistsessentially of the decay portion. In another embodiment, the methodfurther includes comparing the ratio with a predetermined value andidentifying the electrical pulse as a neutron-induced pulse when theratio is at least the predetermined value. In a more particularembodiment, the method further includes comparing the ratio with thepredetermined value and identifying the electrical pulse as a gammaradiation-induced pulse when the ratio is less than the predeterminedvalue. In still another embodiment, the method further includes defininga peak integration window to include a highest reading of the electricalpulse and another reading immediately before or immediately after thehighest reading. In a particular embodiment, the peak integration windowhas a width that is at most 2 ns. In yet another embodiment, the methodfurther includes returning the ratio as a variable and comparing thevariable to a predetermined value. In a particular embodiment, themethod further includes receiving input indicating a value at the pulseanalyzer and changing the predetermined value to the indicated value.

In a further embodiment of the second aspect, the method furtherincludes sending an indicator to a pulse processing device wherein theindicator indicates whether the electrical pulse corresponds to theneutron-induced pulse or to a gamma radiation-induced pulse. In aparticular embodiment, the method further includes sending the indicatorfrom the pulse analyzer via a first output when the electrical pulsecorresponds to the neutron-induced pulse, and sending the indicator viaa second output when the electrical pulse corresponds to the gammaradiation-induced pulse. In a more particular embodiment, the indicatorincludes one or zero when the electrical pulse corresponds to aneutron-induced pulse and the indicator is the other of one or zero whenthe electrical pulse corresponds to a gamma radiation-induced pulse. Inan even more particular embodiment, the method further includesgenerating a neutron spectrum, a gamma radiation spectrum or anycombination thereof, at a pulse processor based on a plurality of ones,zeros, or any combination thereof received from the pulse analyzer.

In another particular embodiment of the second aspect, the indicatorincludes an analog output. In a particular embodiment, the methodfurther includes replicating the first electrical pulse at the pulseanalyzer to form a second pulse, sending one of the first and secondelectrical pulses to a pulse analysis device of the pulse analyzer andsending the other of the first and second electrical pulses to a delaycircuit of the pulse analyzer, and sending a logic pulse from the pulseanalysis device to an output control circuit, when the ratio is at leasta predetermined value. In a more particular embodiment, the methodfurther includes receiving the other of the first and second electricalpulses at the output control circuit after the pulse analysis device hascalculated the integrals, and sending the other of the first and secondelectrical pulses to a first output after receiving the logic pulse fromthe pulse analysis device and sending the other of the first and secondelectrical pulses to the second output when the logic pulse from thepulse analysis device is not received.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

In a particular embodiment, a method may be described in a series ofsequential actions. The sequence of the actions and the party performingthe actions may be changed without departing from the scope of theteachings unless explicitly stated to the contrary. Actions may beadded, deleted, or altered. Also, a particular action may be iterated.Further, actions within a method that are disclosed as being performedin parallel may be performed serially, and other actions within a methodthat are disclosed as being performed serially may be performed inparallel.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Separate embodiments may also beprovided in combination in a single embodiment, and conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range. Many other embodiments may be apparent toskilled artisans only after reading this specification. Otherembodiments may be used and derived from the disclosure, such that astructural substitution, logical substitution, or another change may bemade without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

What is claimed is:
 1. A radiation detection system comprising: aphotosensor to receive light from a scintillator via an input and tosend an electrical pulse at an output in response to receiving thelight; and a pulse analyzer comprising a circuit that is adapted tocalculate the integral over time of at least a portion of a decayportion of an electrical pulse and the integral over time of thecombination of the decay portion and a rise portion of the electricalpulse and to determine whether the electrical pulse corresponds to aneutron-induced pulse, based on a ratio of the integral of at least aportion of the decay portion of the electrical pulse to an integral of acombination of the decay portion and the rise portion of the electricalpulse.
 2. The radiation detection system of claim 1, wherein the pulseanalyzer is configured to compare the ratio with a predetermined valueand to identify the electrical pulse as a neutron-induced pulse when theratio is at least the predetermined value.
 3. The radiation detectionsystem of claim 2, wherein the pulse analyzer is configured to returnthe ratio as a variable and to compare the variable to the predeterminedvalue.
 4. The radiation detection system of claim 1, wherein the decayportion and the rise portion include portions of the electrical pulsethat are at or above a threshold.
 5. The radiation detection system ofclaim 1, wherein the combination of the decay portion and the riseportion includes a peak of the electrical pulse.
 6. The radiationdetection system of claim 1, wherein the combination of the decayportion and the rise portion includes a peak integration window definedby a first time that corresponds to a highest reading of the electricalpulse and a second time that corresponds to a reading that isimmediately before or immediately after the highest reading.
 7. Theradiation detection system of claim 6, wherein a peak integration windowhas a width that is adjustable at the pulse analyzer.
 8. The radiationdetection system of claim 1, wherein the pulse analyzer includes a fieldprogrammable gate array (FPGA).
 9. The radiation detection system ofclaim 1, wherein the pulse analyzer is configured to send an indicatorto a pulse processing device, wherein the indicator indicates whetherthe electrical pulse corresponds to the neutron-induced pulse or to thegamma radiation-induced pulse.
 10. The radiation detection system ofclaim 9, wherein the indicator comprises a first replicate of theelectrical pulse.
 11. The radiation detection system of claim 10,wherein the first replicate comprises an analog replicate of theelectrical pulse.
 12. The radiation detection system of claim 10,wherein the pulse analyzer includes: a splitter to replicate theelectrical pulse and to send the first replicate to a delay circuit andto send a second replicate to a pulse analysis device; and an outputcontrol circuit to receive the first replicate from the delay circuitafter the pulse analysis device has calculated the integrals, whereinthe output control circuit is configured to send the first replicate tothe first output after receiving a logic pulse from the pulse analysisdevice and to send the first replicate to the second output when a logicpulse is not received from the pulse analysis device.
 13. The radiationdetection system of claim 1 wherein the digital logic circuit comprisesa field programmable gate array.
 14. A method comprising: receiving anelectrical pulse at a pulse analyzer from a photosensor of a radiationdetection device; defining a peak integration window to include ahighest reading of the electrical pulse and another reading immediatelybefore or immediately after the highest reading; determining whether theelectrical pulse corresponds to a neutron-induced pulse or a gammaradiation-induced pulse, based on a ratio of an integral of a particularportion of the electrical pulse to an integral of a combination of adecay portion and a rise portion of the electrical pulse, wherein eachof the integrals is integrated over time and the decay portion and therise portion are at or above a threshold; and sending an indicator to apulse processing device, the indicator identifying the electrical pulseas corresponding to a neutron-induced pulse or a gamma radiation-inducedpulse.
 15. The method of claim 14, wherein the particular portionconsists of the decay portion.
 16. The method of claim 14, furthercomprising comparing the ratio with a predetermined value andidentifying the electrical pulse as a neutron-induced pulse when theratio is at least the predetermined value.
 17. The method of claim 14,wherein the peak integration window has a width that is at most 2 ns.18. A method comprising: receiving a first electrical pulse from aphotosensor of a radiation detection device; replicating the firstelectrical pulse to form a second pulse; sending the first electricalpulse to a pulse analysis device and sending the second pulse to a delaycircuit; calculating with the pulse analysis device a ratio of theintegral over time of the particular portion of the first electricalpulse to the integral over time of the total pulse and comparing theratio to a predetermined value, in order to determine whether theelectrical pulse corresponds to a neutron-induced electrical pulse or agamma radiation-induced electrical pulse; and sending a logic pulse fromthe pulse analysis device to an output control circuit indicating thatthe electrical pulse corresponds to a neutron-induced electrical pulsewhen the ratio is at least a predetermined value.
 19. The method ofclaim 18, further comprising: receiving the second pulse at the outputcontrol circuit after the pulse analysis device has calculated theintegrals; and sending the second electrical pulse to a first outputafter receiving a logic pulse from the pulse analysis device indicatingthat the electrical pulse corresponds to a neutron-induced electricalpulse and sending the second pulse to a second output when the logicpulse from the pulse analysis device is not received.
 20. The method ofclaim 18, further comprising: receiving the second pulse at the outputcontrol circuit after the pulse analysis device has calculated theintegrals; and sending the second electrical pulse to a first outputafter receiving a logic pulse from the pulse analysis device indicatingthat the electrical pulse corresponds to a neutron-induced electricalpulse and sending the second pulse to a second output after receiving alogic pulse from the pulse analysis device indicating that theelectrical pulse corresponds to a gamma radiation-induced electricalpulse.